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Heavy Ion Interactions with Matter

Heavy Ion Interactions with Matter. Items : Introduction Electromagnetic dissociation Photon spectrum. Sampling the photon-nucleus cross sections Results of simulation Beam energy loss Summary. George Smirnov. 1 . Introduction.

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Heavy Ion Interactions with Matter

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  1. Heavy Ion Interactions with Matter • Items : • Introduction • Electromagnetic dissociation • Photon spectrum. Sampling the photon-nucleus cross sections • Results of simulation • Beam energy loss • Summary George Smirnov G. Smirnov

  2. 1. Introduction Peripheral heavy-ion collisions: a projectile incident on a target with impact parameter b > R1 + R2  Photon flux proportional toZ2 • Strong electromagnetic field generated by the projectile results in: • electromagnetic dissociation of the target ion • excitation of the projectile nucleus or the nuclear break-up • neutron evaporation in the GDR decay Energetic protons and neutrons emerge : E ~ 3 TeV G. Smirnov

  3. 2. Photon spectrum • One-photon process Ultrarelativistic ions: RHIC:   100 LHC:   3000 • Equivalent photon number (photon spectrum)  ( Leading logarithmic approximation ) G. Smirnov

  4. Photon spectrum in the case of interactions: 1) beam – pipe2) beam – residual gas3) beam – collimator Equivalent photon number vs photon energy: Curve No Projectile Collider 1 Pb LHC 2 Au RHIC 3 Ca LHC G. Smirnov

  5. Photon spectrum in the case of beam-beam interactions • Effective gamma-factor: (a) Symmetric colliding beams eff = 2p2– 1 (b) Asymmetric colliding beams 1,2eff = 1 2(1 + 12) • PbPb LHC • AuAu RHIC • CaCa LHC G. Smirnov

  6. Major problem:development of the procedure of the fast (analytical) integration Can be solved by employing polynomial fits for the real photon cross sections() Next problem: fitting complicated GDR spectra Can be solved by employing Bezier curves 3. Sampling the photon-nucleus cross sections Cross section for the one-(quasi-real) photon process: G. Smirnov

  7. Automatic fitting procedure – allows rapid uprgrade of the cross section database for hundreds of nuclids Input: Experimental points or Lorenzian curves approximating () Output: Four coefficients Pldifining Bezier curves in the interval ij such that P1 = i()andP4 = j() The fitted energy range is typically split in 20 – 30 intervals Systematics introduced by the fit is substantially lower than typical discrepancies between data on photonuclear reactions from different groups, which are in the range from 8 to 25%. Automaticsampling G. Smirnov

  8. 4. Results of simulation – electromagnetic dissociation • FLUKA – green lines • RELDIS – red lines • Projectile: 30 A GeV Pb • Targets: Al, Cu, Sn and Pb • Data points: measurements of forward 1n and 2n emission (H.H. Braun et al. , to besubmitted to NIM) G. Smirnov

  9. Inclusive cross sections evaluated in the DPMJET and FLUKA-ED models Production of the nuclear fragments with charge Z • DPMJET : solid-line histogram (sum of electromagnetic and hadronic contributions) • FLUKA – Electromagnetic Dissociation: dashed-line histogram • Data – blue circles and red squares • Projectile:158 A GeV Pb ions • Tagets: C, Al, Cu, Sn, AuandPb (F. Ballarini et al., SLAC – PUB - 10813) G. Smirnov

  10. 5. Energy loss dE / dx • Ionization • Pair production • slow pairs:E+, E- m • fast pairs:m<< E+, E-<<  m Pfast / Pslow  ln2 ( / mb) For >> 1most of the e+e- pairs will be fast ones Major source of beam loss : total cross section for Pb + Pb at LHC is 200 kb Localized beampipe heating magnet quenching G. Smirnov

  11. Feature of electromagnetic processes induced by heavy ions: Ion charge is large – accuracy of perturbative calculations is not any more determined by the parameter 1 / 137 : it is now Z / 137 Higher order processes are important: d  = d Born + d Coul d Born ~ ln32andd Coul ~ ln22 • some technical problems of theoretical consideration of the e+e- pair production in heavy ion collisions still remain – see e.g. • A.N. Sissakian et al., hep-ph/0412217, 2004; • E. Bartos, S.R. Gevorkian, E.A. Kuraev and N.N. Nikolaev, 2002. G. Smirnov

  12. Feature of the Pb beam at LHC : dominance of the e+e- pair production in dE / dx • Lead-ion beam loss in Al and Cu evaluated with the crange code (Berkeley Range-Energy Calculator) LS – Lindhard-Soerensen theory FNS – Finite nuclear size effects (pair production contribution –calculations by A.H. Soerensen) • More flexible procedure is under development in the framework of FLUKA code G. Smirnov

  13. 5. Summary • Total and 1nX, 2nX electromagnetic dissociation cross sections for Pb-Arelativistic collisions are simulated using FLUKA code • Results of simulution are verified by comparing with cross sections 1nX and 2nX measured in reactions of 30 A GeV Pb ions incident on Al, Cu, Sn and Pb targets • Work in progress: heavy-ion stopping powers in the framework of the FLUKA model (ionization loss in the ultrarelativistic regime, pair production) G. Smirnov

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